Fixes inhale_pp ratio

The amount of inhaled gas used shouldn't approach infinity as inhale_pp
goes to zero, should it?

Also the amount of gas used should decrease with inhale_pp as the
oxyloss is being caused by the fact that fewer moles are entering the
bloodstream.
More sensible oxyloss scaling
Merge pull request #5074 from mwerezak/inhale-ratio-fix

Possible fix fo inhale_pp ratio